Remote vehicle starting systems are widely available in the North-American continent particularly in those areas where the climate is harsh during the winter season. A typical remote vehicle starting system includes a hand-held transmitter with a simple key pad structure that allows the owner of a vehicle to remotely start the engine by depressing the appropriate key. The hand-held transmitter generates a low power radio frequency (RF) signal received by a controller mounted in the vehicle. Once a valid engine start command is recognized the controller energises the starter motor, ignition and fuel supply systems so the engine can be started without any human intervention. To enhance the functionality of such remote vehicle starting systems manufacturers have also built in those devices additional features such as the ability to control the door locks remotely, raise or lower the windows, operate the trunk release lock and activate/deactivate the alarm system of the vehicle, among others. To operate a selected component of the vehicle, the owner must depress a specific key or a combination of keys on the keypad that is unique.
To enable a reliable radio communication between the hand-held transmitter and the controller on board the vehicle, a suitable antenna must be installed on the vehicle. The antenna of a remote vehicle starting system is usually mounted inside the vehicle, at some appropriate location in the cabin. Although installing the antenna outside is possible, such procedure is not preferred for practical reasons. Indeed, if the antenna is connected to a body panel such as the fender or trunk a suitable pathway must be provided to route the antenna cable toward the receiver. Such pathway is difficult to find or create particularly because vehicle manufacturers design automobiles with cabins that are very well isolated from the external environment and in most cases apertures allowing the passage of the antenna cable are nonexistent. Drilling a hole in the body panel to accommodate the antenna cable is of course possible, however, such procedure is objectionable because it creates a permanent alteration to the body panel and increases the risk of corrosion. A different possibility is to use antennas developed for cellular telephony applications that mount to a glass surface and connect with a cable, located in the cabin through a capacitive coupling established through the glass material. This solution is not optimal, however, because the capacitive coupling significantly weakens the radio signal.
A typical internally mounted antenna for a remote vehicle starting system includes a pair of relatively rigid rod-like conductors that project from a housing of plastics material where is placed the demodulator circuit, constructed as a small printed circuit board. The back surface of the housing is provided with an adhesive surface so it can be securely mounted to any appropriate location, such as the inner surface of the windshield.
Two distinct drawbacks exist with this approach. First, the antenna device, constituted by the pair of rigid conductors is not physically separable from the receiver section which means that if one component, either the antenna device or the demodulator fails, the entire unit must be replaced. Second, the antenna/demodulator unit is quite bulky and may not be aesthetically pleasant to the eye.